The present invention relates to an engine cylinder block.
A typical cylinder block for an engine has an upper part including cylinders and a lower part functioning as a crankcase. Japanese Laid-Open Patent Publication No. 2002-97997 describes a cylinder block formed from two parts, a cylinder liner portion and a cylinder block body. The cylinder liner portion forms cylinders, and the cylinder block body forms a crankcase and the outer walls of a water jacket. The water jacket is defined between the cylinder liner portion and the cylinder block body. The cylinder liner portion connects the peripheral surfaces of a plurality of cylindrical cylinder liners.
In a cylinder liner portion of such a two-part cylinder block, the walls defining cylinders may be integrally formed with an upper deck, which receives a cylinder head and which is fastened to the cylinder block body. With a two-part cylinder block having such a structure, the upper section of the cylinder liner portion is securely fastened to the cylinder block body.
However, in comparison with the upper section, the lower section of the cylinder liner portion has less rigidity. As a result, the thermal expansion and vibrations that occur during the combustion of air-fuel mixture may lead to thermal distortion or deformation. Such deformation or distortion may increase the slide resistance of pistons and affect engine performance in an undesirable manner.